1. Field of the Invention
The present invention relates to an engine valve train in which inlet valves are driven to open and close by a camshaft supported on a camshaft holder via inlet rocker arms, in which a stem end of the inlet valve is pressed against by a holding rod connected to an armature of an electromagnetic actuator mechanism so as to hold the inlet valve in an open state, and in which an impact is absorbed by a hydraulic damper mechanism which is generated by the inlet valve when the inlet valve is released from being held by the electromagnetic actuator mechanism so as to be restored to a closed state and is then seated.
2. Description of the Related Art
Among engine valve trains of the aforesaid type, disclosed in JP-A-63-295812 is an engine valve train in which hydraulic damper mechanisms are disposed within an upper space of a valve chamber.
Incidentally, an attempt at using special supporting members to support hydraulic damper mechanisms causes a problem in that the number of components involved is increased. Then, to cope with this problem, an attempt at using a head cover to support the hydraulic damper mechanisms causes problems that the fixing rigidity is deteriorated and that a dimension of an engine in a height direction is increased. In addition, an attempt at using a cylinder head to support the hydraulic damper mechanisms causes problems in that the dimension of the engine in in the height direction is increased and that the working of the cylinder head becomes complicated because of oil passages which communicate with the hydraulic damper mechanisms having to be formed.
The present invention was made in view of the above situations and an object thereof is to provide a means for supporting the hydraulic damper mechanisms of the engine valve train in a strong and compact manner.
With a view to attaining the object, according to a first aspect of the present invention, there is proposed an engine valve train having: a camshaft supported on a camshaft holder and driving inlet valves to open and close via inlet rocker arms; an electromagnetic actuator mechanism including an armature; a holding rod connected to the armature and pressing against a stem end of the inlet valve so as to hold the inlet valve in an open state; and, a hydraulic damper mechanism absorbing an impact which is generated by the inlet valve when the inlet valve is released from being held by the electromagnetic actuator mechanism so as to be restored to a closed state and is then seated, wherein the hydraulic damper mechanism is supported on the camshaft holder.
According to the construction, the hydraulic damper mechanism is adapted for absorbing the impact generated by the inlet valve, when the inlet valve is released from being held by the electromagnetic actuator mechanism so as to be restored to a closed state and then seated, and is supported on the camshaft holder. Therefore, it is not only the necessity of a special support member obviated to thereby reduce the number of components involved, but also that oil passages which communicate with the hydraulic damper mechanisms can be formed in the camshaft holder to thereby facilitate the working of the cylinder head. In addition, when compared with the case where the hydraulic damper mechanisms are mounted on the head cover, the fixing rigidity can be enhanced, and the dimension of the engine in the height direction can be reduced. Furthermore, when compared with the case where the hydraulic damper mechanisms are mounted on the cylinder head, the cylinder head can be made smaller in size.
According to a second aspect of the present invention, there is proposed an engine valve train as set forth in the first aspect of the present invention, wherein the camshaft holder is an integrated body connected together in a direction in which a plurality of cylinders are arranged, and wherein the hydraulic damper mechanism is provided at a connecting portion of the camshaft holder.
According to the construction, since the hydraulic damper mechanism is provided at the connecting portion of the integrated camshaft holder which is connected together in the direction in which the plurality of cylinders are arranged, the hydraulic damper mechanism is allowed to be mounted on the portion of the camshaft holder which has a high rigidity to thereby enhance the fixing rigidity.
According to a third aspect of the present invention, there is proposed an engine valve train as set forth in the first or second aspect of the present invention, wherein the hydraulic damper mechanism is provided coaxially with and below the electromagnetic actuator mechanism, and wherein the hydraulic damper mechanism is accommodated in the interior of the camshaft holder.
According to the construction, since the hydraulic damper mechanism is accommodated in the interior of the camshaft holder in such a manner as to be situated below the electromagnetic actuator mechanism, not only the dimension of the engine in the height direction can be reduced, but also the fixing rigidity of the hydraulic damper mechanism can be enhanced further.
According to a fourth aspect of the present invention, there is proposed an engine valve train as set forth in the third aspect of the present invention, wherein the hydraulic damper mechanism is provided with a holding rod passage hole through which the holding rod of the electromagnetic actuator mechanism is allowed to pass, the holding rod passage hole also functioning as a vent hole for venting air from an oil chamber of the hydraulic damper mechanism.
According to the construction, since the holding rod passage hole which is provided in the hydraulic damper mechanism so as to allow the holding rod of the electromagnetic actuator mechanism to pass therethrough functions as a vent hole for venting air from the oil chamber of the hydraulic damper mechanism, air in the oil chamber can be vented without providing any special vent hole for that purpose.
According to a fifth aspect of the present invention, there is proposed an engine valve train as set forth in the first aspect of the present invention, further having: a pair of armature fixing mechanisms disposed in the interior of the camshaft holder so as to hold the hydraulic damper mechanism.
According to a sixth aspect of the present invention, there is proposed an engine valve train as set forth in the fifth aspect of the present invention, wherein each armature fixing mechanism includes a cylinder formed in the camshaft holder, a piston which slidably fits in the cylinder, a return spring for biasing the piston upwardly, an oil chamber formed in an upper surface of the piston and an armature locking member which protrudes upwardly from the upper surface of the piston for abutment with a lower surface of a projection from the armature.
Note that first and second inlet rocker arms 30, 31 correspond to the rocker arms of the present invention.